1. Field of the Invention
The present invention relates to an information transmission system that is formed by connecting electronic apparatuses by using two kinds of different interfaces, that is, an interface enabling sending and reception of control information such as a digital interface according to the IEEE 1394 standard and an interface enabling transmission of only an information signal such as an analog interface, as well as to an information output apparatus, an information input apparatus, and a connection relationship identification method that are used in such an information transmission system.
2. Description of the Related Art
In recent years, various digital contents have come to be provided abundantly via communication media such as broadcast media and the Internet and via recording media such as the DVD (digital video disc). It is now being considered how to broaden the range of use of digital contents that have come to be provided abundantly and how to prepare an environment in which users can use digital contents conveniently.
For example, it is now being considered to provide a digital interface in electronic equipment generically called audio-visual (AV) equipment such as a monitor receiver and various kinds of reproducing apparatuses, recording apparatuses, recording/reproducing apparatuses, and receiving apparatus. Providing a digital interface in various kinds of electronic equipment in this manner makes it possible to transmit digital contents between various electronic apparatuses and to reproduce or copy digital contents without deteriorating those.
Among a variety of digital interfaces, the IEEE 1394 standard digital interface is now attracting much attention which has been standardized by the IEEE (The Institute of Electrical and Electronics Engineers, Inc. (U.S.)) and enables high-speed transmission of a digital video signal, a digital audio signal, etc. that require real-time processing.
According to the IEEE 1394 standard digital interface, information is transmitted by packet transmission. Providing a high degree of freedom of connection between electronic apparatuses, the IEEE 1394 standard digital interface enables tree wiring, star wiring, daisy chain wiring, etc.
Where electronic apparatuses having an IEEE 1394 standard digital interface are connected to each other in daisy chain form as shown in FIG. 1A, the system is equivalent to a system in which a plurality of electronic apparatuses are connected to a single digital bus as shown in FIG. 1B.
In FIGS. 1A and 1B, an IRD (integrated receiver decoder) 1 is a receiver capable of receiving a digital satellite broadcast etc. DVTRs 3 and 4 are, digital video tape recorders, and a DVD apparatus 4 is a recording/reproducing apparatus, for example, of a DVD (digital video disc).
In the example of FIGS. 1A and 1B, the plurality of electronic apparatuses can send digital data to a common digital bus 6. Digital data that are sent to the digital bus 6 can be distinguished from each other by channel Nos. that are prescribed in the IEEE 1394 standard digital interface.
A node ID for identifying an electronic apparatus as an output source of digital data is described in the header portions of packets that are used for transmission of the digital data. Therefore, by using a channel No. and a node ID, an electronic apparatus to be supplied with digital data can easily receive necessary digital data from a target electronic apparatus.
In the case of the IEEE 1394 standard digital interface, information of a digital input/output terminal of each electronic apparatus is described as plug information or stored by a mechanism called a descriptor in an internal register of a digital interface circuit that is provided in each apparatus. Therefore, each apparatus can manage the connection state by correlating, one-to-one, digital input/output terminals of respective electronic apparatuses with information of the internal register of the self apparatus.
As described above, in the case of the IEEE 1394 standard digital interface, not only specific information (identification information) or the like of an electronic apparatus but also various kinds of control information can be transmitted. Further, it is possible to send digital data to a target electronic apparatus via a common digital bus and to receive digital data from a target electronic apparatus via a common digital bus.
For example, it is now being considered to prepare an environment in which users can use digital contents conveniently by making it possible to easily construct what is called a home network system that enables mutual information exchange by connecting various AV apparatuses, a personal computer, etc. in a home as shown in FIGS. 1A and 1B by using IEEE 1394 standard digital interfaces.
Incidentally, as described above, although various electronic apparatuses have come to be provided with a digital interface, they need to be provided also with a conventional analog interface. This is because not all contents are provided in the form of a digital signal.
For example, conventional analog broadcast is still performed though digital broadcast has come to be performed. As long as only broadcast media are concerned, it is considered that contents will continue to be provided for the time being by both analog signals and digital signals. Further, there is a demand that not only digital contents but also information resources that have been obtained through conventional analog interfaces be kept usable.
For the above-described reasons, one option is to provide various electronic apparatuses with both of an analog interface and a digital interface. In this case, various electronic apparatuses can be connected to each other in a large number as shown in FIGS. 1A and 1B.
For example, it is one option to provide an information input apparatus such as a monitor receiver that accepts input of an information signal such as a video signal from various electronic apparatuses with a plurality of analog input terminals to enable it to accept input from a plurality of electronic apparatuses.
The information input apparatus that is an electronic apparatus connected to a system via an IEEE 1394 standard digital interface is so configured as to be able to reliably receive intended digital data from a target electronic apparatus by, for example, a user's merely specifying the target electronic apparatus to output the intended digital data.
As described above, in the case of the digital interface (serial bus plug) that enables sending and reception of specific information of an electronic apparatus and control information, a connection relationship between electronic apparatuses can be identified clearly by using various kinds of information included in digital data.
In contrast, in an information input apparatus having a plurality of analog input terminals, to perform analog input terminal switching (selection), a user needs to remember what electronic apparatuses are connected to what analog input terminals and manipulate an input switching switch provided on a remote commander, for example, of the information input apparatus based his memory. That is, an analog input terminal to which a target electronic apparatus would be connected is selected by switching among pieces of terminal information stored in the information input apparatus in what is called a toggle method by the user's manipulating the input switching switch.
The reason why it is necessary to rely on a manual manipulation of a user is that an electronic apparatus cannot identify a connection relationship between electronic apparatuses because an analog interface (external plug) is for output or input of only an analog information signal and an analog information signal does not include specific information of an electronic apparatus or control information.
In the above-configured information input apparatus having a plurality of analog input terminals, time and labor are needed to correctly identify an input terminal that should receive an analog signal from a target electronic apparatus. Further, when the information input apparatus having a plurality of analog input terminals is to be supplied with an analog signal from a target electronic apparatus, there may occur a trouble that a wrong electronic apparatus is selected and an analog signal that is different from an intended one is supplied.